The purpose and scope of this project is subdivided in two specific aims that are detailed below: Specific Aim 1: Develop Multifunctional Liposomes with Targeting and Imaging Capabilities Liposomes are biocompatible and can entrap water-soluble (hydrophilic) pharmaceutical agents in their internal water compartment and water-insoluble (hydrophobic) reagents into the membrane. The liposome-incorporated pharmaceuticals are protected from the inactivating effect of external conditions; yet do not cause undesirable side reactions. Moreover, liposomes have the ability to deliver pharmaceuticals into cells or even inside individual cellular compartments. In addition, the size, charge and surface properties of liposomes can be modified by adding new ingredients to the lipid mixture before liposome preparation and/or by variation of preparation methods. It is possible to attach to the liposome surface specific ligands and hydrophilic polymers with highly flexible chains results in long-circulating liposomes. Moreover, incorporation of positively charged lipid derivatives or positively charged polymers allows for DNA binding and efficient cell transfection. Attachment of certain proteins and peptides (usually monoclonal antibodies or their Fab fragments) to the liposome surface may target nanoparticles to certain pathological areas in the body or inside cells. We use our understanding of viral fusion mechanisms to devise nano fusion machines by exploiting a new class of fusion-associated small transmembrane proteins. Specific Aim 2: Develop Multifunctional Triggering Modalities An important requirement for effective drug delivery is the precise spatial and temporal release of therapeutic agents at the target site. A variety of chemical and physicochemical approaches have been devised to create lipid-based nanoparticles that can be triggered to release their contents in a controlled fashion. The stimuli to induce release can be divided into systems triggered by an externally applied stimulus such as heat or light, and those triggered by a biologically supplied stimulus such as the drop of pH, enzymatic cleavage, or change of a redox potential. The chemical components that respond to these stimuli and induce the liposome leakage include ionizable lipids, lipids with a desired phase transition temperature (melting temperature), cleavable lipids, functional ionizable polymers and peptides, ionizable detergents, cis-trans isomerization, and free-radical-generating compounds as photosensors. The modern advances in focused ultrasound technology will enable the release an entrapped drug preferentially at temperatures attainable by mild local hyperthermia. We have designed strategies to directly activate hydrophobic cytostatic agents that target trans-membrane proteins. Scintillator crystals will be used as mediators that will convert the ionizing radiation into visible UV light which in turn will activate cytostatic to kill tumor cells.